Engines operating with one or more cylinders as dedicated exhaust gas recirculation (EGR) cylinders enjoy greatly simplified controls and pressure management, fewer hardware devices, and other benefits. However, these simplifications come at the cost of a loss of control over the system, including a loss of control of the EGR fraction during low load and transient conditions. When nominal cylinders are dedicated to providing EGR, and standard fueling and controls are applied, the target EGR fraction in the charge flow provided by the cylinders is determined by the simple ratio of the number of EGR cylinders to the total number of cylinders. For example, an engine with one cylinder dedicated to EGR and four cylinders total will operate at a 25% EGR fraction if all of the cylinders are operated in the same manner.
However, during transient conditions the pressure of the charge flow in the intake manifold fold is able to change more rapidly than the pressure of the exhaust in the exhaust manifold of the dedicated EGR cylinder(s). As a result, the EGR fraction that is actually provided can increase significantly over the target EGR fraction during transient conditions. When the EGR fraction increases or deviates from its expected or target value, cylinder misfire and combustion instability can result. Therefore, further technological developments are desirable in this area.